In rotary piston mechanisms of various types having multi-lobe housing cavities, such as those described in the U.S. patents to Wankel et al., U.S. Pat. No. 2,988,065 dated June 13, 1961; Nubling, U.S. Pat. No. 2,866,417 dated Dec. 30, 1958; Kraic et al., U.S. Pat. No. 3,323,498 dated June 6, 1967; Kolbe et al., U.S. Pat. No. 3,671,154 dated June 20, 1972; Batten, U.S. Pat. No. 2,873,250 dated Mar. 25, 1975; Huf, U.S. Pat. No. 3,797,974 dated Mar. 19, 1974 and Huf, U.S. Pat. No. 3,923,430 dated Dec. 2, 1975, the working chambers formed between the rotor and the housing cavity walls are isolated from each other and surrounding areas by a sealing grid assembly comprising side wall sealing means and apex seals carried by the rotor or non-rotating seal elements disposed at the junctions of the housing cavity lobes. Heretofore, it was not considered possible to provide optimum volumetric efficiency by employing both apex seals and non-rotating seal elements (hereinafter referred to as "waist seals") because of the rapid failure of the seals due to the accumulative effects of repeated impacts between the apex seals and the non-rotating seal elements. While counterweighted apex seals which function to retract at the lobe junctures are known and disclosed in various U.S. patents, such as the patents to Jones, U.S. Pat. No. 3,456,626 dated July 22, 1969; Jones, U.S. Pat. No. 3,482,551 dated Dec. 9, 1969 and Kumar, U.S. Pat. No. 3,909,013 dated Sept. 30, 1975, the use of such apex seals in combination with waist seals would not eliminate the impact problem without an appreciable increase in leakage or blow-by at the apex seals. The prior art teaching, as exemplified in the U.S. Pat. No. 3,873,250 to Batten, and the French Pat. No. 590,085 to Planche, dated June 10, 1925, which disclose the pressurization of the apex seals to bias them outwardly of the grooves, even at the lobe junctures, obviously do not provide a solution to the impact problem.
Accordingly, it is an object of the present invention to provide an improved seal grid assembly for a rotary piston mechanism of the multi-lobe type which grid assembly includes both apex seals and waist seals.
Another object is to provide for a rotary piston mechanism of the multi-lobe type, an improved sealing grid assembly which effects an increase in the volumetric efficiency of the rotary piston mechanism as compared with mechanisms having heretofore known seal grid assemblies.
A still further object of this invention is to provide an improved seal grid assembly for a rotary piston mechanism of the multi-lobe type, having waist seals, which assembly includes apex seals each of which are capable of automatically moving between a retracted position where it is out of engagement with the peripheral wall of the multi-lobe cavity of the mechanism and an extended position where it is in engagement with the peripheral wall of the cavity to avoid thereby impacts between the apex seal and the waist seals.